1. Field of the Invention
The present invention relates to a process for supplying a rare earth metal-based alloy powder to a cavity in a mold, for example, in order to subject the rare earth metal-based alloy powder to a pressing for producing a rare earth metal-based magnet, and to an apparatus suitable for use in such process. More particularly, the present invention relates to a powder supplying process which is capable of uniformly supplying and filling, into a cavity, even an alloy powder which is poor in flowability and difficult to be filled in a cavity and moreover, is inflammable and difficult to handle, as is the above-described rare earth metal-based alloy powder, without production of agglomerates and bridges and without occurrence of inflammation.
2. Description of the Related Art
To supply a powder poor in flowability from a feeder box into a cavity in a mold, a supplying apparatus is conventionally used, which is designed so that a feeder box having an opening in its bottom is moved to above a cavity defined in a mold, whereby a rare earth metal-based alloy powder is supplied from the feeder box into the cavity. There are such conventionally known powder supplying apparatus in which a rotary blade rotated in the feeder box is used as described in Japanese Patent Application Laid-open No. 59-40560; a spherical member rotated in the bottom of the feeder box, as described in Japanese Patent Application Laid-open No. 10-58198; or a rotary blader rotated spirally within the feeder box is used, as described in Japanese Utility Model Application Laid-open No. 63-110521.
In the above prior art systems; however, the height of the feeder box is increased, and the stroke of a punch is prolonged. Therefore, the time taken for one run of the pressing is prolonged, resulting in a reduced productivity. A powder poor in flowability such as a rare earth metal-based alloy powder cannot be filled uniformly into the cavity, if a uniform urging force is not provided. Particularly a rare earth metal-based alloy powder produced by a strip casting process and having an excellent magnetic characteristic is extremely poor in flowability and difficult to be filled uniformly into the cavity, because it has a small average particle size and a narrow and sharp distribution of particle sizes. Further, when a lubricant such as a fatty ester for enhancing the orientation is added, the alloy powder has an increased viscosity, and hence, is more difficult to be filled uniformly into the cavity.
In addition, in the apparatus having the above-described arrangement, there is a possibility that the rare earth metal-based alloy powder is exposed to the atmosphere to become inflamed, because each of the die surface and the bottom of the feeder box is formed of a metal, and the alloy powder is sometimes caught between them.
Accordingly, it is an object of the present invention to provide a powder supply process and apparatus for supplying an alloy powder from a feeder box having an opening in its bottom into a cavity defined in a mold by moving the feeder box to above the cavity, wherein even a powder difficult to handle such as a rare earth metal-based alloy powder can be supplied from the feeder box into the cavity under a uniform pressure, as compared with the conventional agitation means, without a fear of inflammation.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an apparatus for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom surface into a cavity by moving the feeder box to above the cavity, the apparatus comprising a bar-shaped member which is moved horizontally and in parallel in the bottom of the feeder box.
With the above feature, the powder in the feeder box is supplied into the cavity, while reciprocally moving the bar-shaped member in the horizontal direction in the bottom of the feeder box. Therefore, the powder in the feeder box can be supplied into the cavity under a uniform pressure sequentially in an order of from a powder portion present in the vicinity of the bottom to a portion present in the top of the box, and filled with a uniform density without production of agglomerates and bridges.
According to a second aspect and feature of the present invention, in addition to the first feature, a plurality of the bar-shaped members are provided horizontally at distances.
With the above feature, the plurality of the bar-shaped members are provided horizontally at distances and therefore, the alloy powder can be filled more efficiently into the cavity.
According to a third aspect and feature of the present invention, in addition to the second feature, the distance between the bar-shaped members is generally equal to a distance between cavities arranged in a plurality of rows in a direction of arrangement of the bar-shaped members.
With the third feature, the uniform supplying and filling of the powder into each of the cavities disposed in the plurality of rows can be achieved by each of the bar-shaped members. Even if the finally stopping position for the bar-shaped member after the parallel movement thereof has been failed to be established at a point offset from the opening surface of the cavity, each of the bar-shaped members is stopped at the same position relative to each of the cavities and hence, the supplying and filling of the powder can be carried out, so that a variability in amount of alloy powder filled in the cavities is not produced for each of the cavities.
According to a fourth aspect and feature of the present invention, in addition to the first feature, the bar-shaped member is of an arcuate shape in section.
With the fourth feature, the section of the bar-shaped member is of the arcuate shape, but may be of any of polygonal shapes such as triangular, quadrilateral and pentagonal shapes and the like. However, if the section of at least lower half of the bar-shaped member for guiding the alloy powder is of an arc-shape of a circle or an ellipse, the alloy powder coming into contact with the bar-shaped member with the horizontal movement of the bar-shaped member is guided into the cavity, while being moved downwards along a peripheral surface of the bar-shaped member, whereby the supplying and filling of the powder into the cavity can be achieved under an extremely uniform pressure.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the bar-shaped member has a diameter in a range of 0.3 to 7 mm.
With the above feature, the diameter of the bar-shaped member is in the range of 0.3 to 7 mm. However, if the diameter of the bar-shaped member is smaller than 0.3 mm, the urging force is insufficient. On the other hand, if the diameter exceeds 7 mm, the pressure applied to the alloy powder during horizontal movement of the bar-shaped member is too high and produces agglomerates in the alloy powder.
According to a sixth aspect and feature of the present invention, in addition to the first feature, the bar-shaped member is disposed, so that the distance between its lower end and a die surface at a peripheral edge of the opening in the cavity is from 0.2 to 5 mm.
With the above feature, the lower end of the bar-shaped member is spaced at a distance of 0.2 to 5 mm apart from the die surface at the peripheral edge of the opening in the cavity. This is because if the distance is smaller than 0.2 mm, the alloy powder is pressed between the die surface at the edge of the opening in the cavity and the bar-shaped member and produces agglomerates in the alloy powder. On the other hand, if the distance exceeds 5 mm, an effect for urging the alloy powder into the cavity under a uniform pressure is not obtained.
According to a seventh aspect and feature of the present invention, an addition to the first feature, another bar-shaped member is also provided at a location above the bar-shaped member provided in the first feature, so that it is moved horizontally and in parallel in the feeder box.
With the above feature, the other bar-shaped member is provided at the location above the bar-shaped member provided in the first feature. Therefore, the unevenness of the alloy powder generated within the feeder box by the supplying of the powder can be eliminated, and the gravitational filling pressure can be uniformized. In addition, the agglomerates produced in the alloy powder in the feeder box can be clashed.
According to an eighth aspect and feature of the present invention, in addition to the first feature, the finally stopping position for the bar-shaped member after the parallel movement is established at a point offset from the opening surface of the cavity.
With the above feature, it is avoided that the finally stopping position for the bar-shaped member after the parallel movement is at any point above the opening surface of the cavity. Therefore, if the bar-shaped member is stopped at above the opening in the cavity, a variability in density is generated in the front and rear portions in the direction of movement of the bar-shaped member, but according to the present invention, it is possible to prevent a high-density portion and a low-density portion from being formed in the rare earth metal-based powder in the cavity. Therefore, it is possible to prevent the cracking of a compact or a sintered product due to the variability in density.
According to a ninth aspect and feature of the present invention, in addition to the first feature, the apparatus further includes a powder replenishing device for replenishing the alloy powder into the feeder box in an amount corresponding to a decrement in amount resulting from the supplying of the alloy powder from the feeder box to the cavity.
With the above feature, the amount of the alloy powder within the feeder box can be maintained constant at all times, and the gravitational filling pressure is not varied, whereby the amount of alloy powder supplied from the feeder box into the cavity is uniformized.
According to a tenth aspect and feature of the present invention, there is provided an apparatus for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom into a cavity by moving the feeder box to above the cavity, the apparatus comprising an inert gas supply device for filling an inert gas into the powder feeder box.
With the tenth feature, the rare earth metal-based alloy powder can be supplied into the cavity, while maintaining the inside of the power feeder box in an inert gas-filled state by provision of the inert gas feeding device for filling an inert gas into the feeder box. In this case, a friction heat generates an inflammable state with the movement of the feeder box and the movement of the bar-shaped member. However, there is no fear of inflammation.
According to an eleventh aspect and feature of the present invention, there is provided an apparatus for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom into a cavity by moving the feeder box to above the cavity, the apparatus comprising a plate member made of a fluorine-contained resin and mounted on the bottom surface of the feeder box.
With the eleventh feature, the risk of inflammation can be reduced by the mounting of the plate member of the fluorine-contained resin on the bottom surface of the feeder box. More specifically, the bottom surface of the feeder box is violently rubbed against a base plate and the die with the reciprocal movement of the feeder box, and the feeder box is moved, while bringing the alloy powder into contact with the base plate. Therefore, if the bottom surface of the feeder box is formed of the same metal as a material for a side face, e.g., a stainless steel (SUS304), the bottom surface of the feeder box is poor in close contact with the base plate and thus, a portion of the alloy powder is bitten between the bottom surface of the feeder box and the base plate. For this reason, even if the inside of a powder accommodating area is put in an inert gas atmosphere, there is a high risk of inflammation. In addition, there is a possibility that a difference in level is generated between the mold and the die set, and a spark is generated between the feeder box and the die set, resulting in a risk of inflammation. Therefore, by mounting the plate member made of a material such as a fluorine-contained resin permitting a good close contact on the bottom surface of the feeder box, it is possible to prevent a portion of the alloy powder from being bitten between the bottom surface of the feeder box and the base plate, and further, a spark is never generated.
According to a twelfth aspect and feature of the present invention, there is provided a process for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom into a cavity by moving the feeder box to above the cavity, wherein the rare earth metal-based alloy powder within the feeder box is supplied into the cavity, while reciprocally moving a bar-shaped member adapted to be moved horizontally in parallel in the bottom of the feeder box.
According to a thirteenth aspect and feature of the present invention, in addition to the twelfth feature, the rare earth metal-based alloy powder contains a lubricant added thereto.
According to a fourteenth aspect and feature of the present invention, in addition to the twelfth feature, the rare earth metal-based alloy powder is produced by a strip casting process.
According to a fifteenth aspect and feature of the present invention, in addition to the twelfth feature, the bar-shaped member is moved in parallel in a direction perpendicular to a lengthwise direction of the opening of the cavity.
According to a sixteenth aspect and feature of the present invention, in addition to the twelfth feature, the feeder box is retreated in a direction perpendicular to a lengthwise direction of the opening of the cavity after supplying of the alloy powder from the feeder box to the cavity.
According to a seventeenth aspect and feature of the present invention, in addition to the twelfth feature, when the feeder box is moved to above the cavity, the bar-shaped member is located in a front portion of the feeder box in a moving direction of the feeder box.
According to an eighteenth aspect and feature of the present invention, in addition to the twelfth feature, a position for stopping the feeder box moving to above the cavity is established at a location where the center of the feeder box is beyond the center of the cavities in the moving direction of the feeder box.
According to a nineteenth aspect and feature of the present invention, in addition to the twelfth feature, the alloy powder is replenished into the feeder box in an amount corresponding to a decrement in amount of the alloy powder resulting from the supplying of the alloy powder from the feeder box into the cavity.
According to a twentieth aspect and feature of the present invention, there is provided a process for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom into a cavity by moving the feeder box to above the cavity, wherein the feeder box is retreated in a direction perpendicular to a lengthwise direction of the opening of the cavity after supplying of the alloy powder from the feeder box to the cavity.
According to a twenty first aspect and feature of the present invention, in addition to the twentieth feature, the rare earth metal-based alloy powder contains a lubricant added thereto.
According to a twenty second aspect and feature of the present invention, in addition to the twentieth feature, the rare earth metal-based alloy powder is produced by a strip casting process.
According to a twenty third aspect and feature of the present invention, there is provided a process for supplying a rare earth metal-based alloy powder from a feeder box having an opening in its bottom into a cavity by moving the feeder box to above the cavity, wherein the feeder box is moved to above the cavity, while filling an inert gas into the feeder box, thereby supplying the rare earth metal-based alloy powder into the cavity.
According to a twenty fourth aspect and feature of the present invention, in addition to the twenty third feature, the rare earth metal-based alloy powder contains a lubricant added thereto.
According to a twenty fifth aspect and feature of the present invention, in addition to the twenty third feature, the rare earth metal-based alloy powder is produced by a strip casting process.
With the above process, it is preferable that the bar-shaped member 21 is moved in parallel in the direction perpendicular to the lengthwise direction of the opening of the cavity 4 which is defined by a die hole 2b in a die 2a and a lower punch 2, as shown in FIG. 14. This is due to the following reason: When the bar-shaped member 21 is moved in parallel in the lengthwise direction of the opening of the cavity 4, as shown in FIGS. 15 and 16, the alloy powder m in the cavity 4 is pulled in the moving direction with the movement of the bar-shaped member 21, as shown in FIG. 15, because the alloy powder m lacks in flowability. As a result, a variability in density of the alloy powder m supplied into the cavity 4 is liable to be generated in the lengthwise direction. If the variability in density of the alloy powder m is generated in the lengthwise direction, as described above, a variability in size of a sintered product resulting from a sintering step is also generated in the lengthwise direction. However, when the bar-shaped member 21 is moved in parallel in the direction perpendicular to the lengthwise direction of the opening of the cavity 4, the movement of the alloy powder m within the cavity 4 is limited because of a short distance between walls of the cavity 4 which are located at the front and rear portions of the bar-shaped member 21 in the moving direction. Therefore, the variability in density of the alloy powder m within the cavity 4 is difficult to generate, and even if a variability of density of the alloy powder is generated to a small extent, such variability of this extent is corrected by a pressing and hence, a variability in size of the sintered product is not generated.
A variability in density of the alloy powder in the lengthwise direction of the opening of the cavity as described above is also generated upon the retreating movement of the feeder box with the same phenomenon. Therefore, the direction of the retreating movement of the feeder box is also defined as a direction perpendicular to the lengthwise direction of the opening of the cavity 4, whereby the variability in size of the sintered product can be inhibited to inhibit the variability in density of the alloy powder.
When the feeder box is to be moved to above the cavity, if the bar-shaped member is located at a fore end in the moving direction, it is possible to retain the alloy powder in the front portion of the feeder box in the direction of movement of the feeder box. Therefore, it is possible to prevent the alloy powder from being moved and offset backwards as viewed in the advancing direction by the movement of the feeder box, thereby preventing the amount of the alloy powder from being insufficient in the front portion of the feeder box. Thus, the gravitational filling pressure can be uniformized.
The amount of the alloy powder may be insufficient in the front portion of the feeder box and excessive in a rear portion of the feeder box with the movement of the feeder box. Therefore, when the feeder box is moved to above the cavity, it is moved to the location where the center thereof is beyond the center of the cavities. This facilitates the filling of the alloy powder into the cavity under a uniform pressure.
Thus, with the alloy powder supplying process and apparatus according to the present invention, even a rare earth metal-based alloy powder containing a lubricant added thereto, even a rare earth metal-based alloy powder having a viscosity and extremely poor in flowability and in agitatability, even a rare earth metal-based alloy powder produced by the strip casting process, and even a rare earth metal-based alloy powder extremely poor in flowability because of a narrow and sharp distribution of particle sizes, can be supplied into the cavity with an extremely uniform filled density without production of agglomerates and bridges and with no fear of inflammation.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.